This invention relates to a vehicle crash cushion for decelerating a vehicle that has left a roadway and is moving toward a wall.
Young U.S. Pat. No. 3,672,657 (assigned to the assignee of the present invention) discloses a vehicle crash cushion of the general type defined above. The Young system includes an array of parallel diaphragms with water-filled energy absorbing elements between the diaphragms. The outermost diaphragms are arranged to overlap, and the entire assembly is mounted to slide on slide plates perpendicular or adjacent to a wall. An impacting vehicle will move the outermost diaphragms toward the wall, thereby accelerating water in the energy absorbing elements. In this way, the severity of the impact between the vehicle and the wall is substantially reduced.
The Young crash cushion has shown itself to be quite effective in actual use. In one installation the Young crash cushion was placed on a wall at a freeway turn in Detroit. Over ten years of practical experience have shown a substantial reduction in serious injuries and fatalities.
Nevertheless, the Young crash cushion is not without drawbacks, primarily with respect to the level of maintenance required to maintain the crash cushion in an operational condition. It has been found that there is a tendency for the outermost diaphragms not to return to the original position after an impact. In some applications this may require that an entire freeway be shut down while the outer diaphragms are pulled back to the operational position. In practice there is a tendency to delay such maintenance, and the diaphragms themselves are more susceptible to damage if hit by a second impact at a time when they have not recovered properly from the first. Furthermore, the Young crash cushion includes a number of interior diaphragms which are susceptible to damage in a severe impact. Certain elements are formed of wood, which are susceptible to water damage and rotting, and debris such as sand and litter tends to be trapped within the system. It is difficult to remove this debris, and excessive sand can build up inside the unit and interfere with the operation of the crash cushion.
The present invention is directed to an improved vehicle crash cushion which is less susceptible to the maintenance problems of the Young crash cushion described above.